Hesitation

[Mardle]

Ford Galaxy 1.9 TDI Ghia 115bhp. 96K

 

I have a problem with hesitation while accelerating. I had just refurbished the Aux run on pump as per instructions on another post. This worked fine but since I completed the work the car hesitates in first and sometimes second gear. Typical symptom when pulling away from junction car will accelerate well initially. Then it will suddenly have a drop in power, as if you have closed the throttle to a small opening. Within two seconds or less it will then pull really well again. This pattern is sometimes repeated, so pull hesitate pull hesitate. It only seems to do it when the revs are increasing quickly. Never does it in third or any higher gear. I can't see how the aux pump would be related but I have checked the pipes that run in the same area and can't see anything wrong. Other than this the car is fine. MPG is normal, doesent miss, even when the power is reduced the engine is still smoth.

 

Any ideas?

[Mardle]

Advice please. I din't get any responses to my first posting, hesitation, is this beacause I have missed something obvious / essential? Might just be an unusual problem. I have owned three Galaxy's over the last 10 years and this is the first time that I have experienced the problem, its starting to be a bit concerning now especially if you pull away from a roundabout. Thanks.

[Smilge]

If you dont get any responses m8 ..... just add your own reply to the same thread and stick the "BUMP" text in the box .... that'll keep it on the board so people get a chance to have a look and reply.

[NikpV]

as bleeno says just add apost to the topic saying 'bump' or 'anyone?' to bring the post back to the top - I have merged the topic to keep the posts together

[Mardle]

Thanks for the advice.

[Dave-G]

without a fuller description It could be that none of us feel we can offer meaningfull help on this particular fault. This baulk is only occuring when under accelleration - what if you were not to accellerate while the fault is occuring - does it still occur? Is it auto or manual?

[Smilge]

Sounds to me like the throttle position sensor as i had a similar problem on my Mondeo .... dont quote me but there are numerous things that could cause these symptoms ...... checked all the vacuum pipes?

[tim-spam]

Another possibility is the VNT mechanism on the turbo being a little sticky.

 

Basically, as the revs increase, the turbo boost increases, and as the engine speed approaches around 2000rpm, the VNT mechanism starts to back off to keep the boost at the correct level, determined by the ECU. There is a T-MAP sensor, which measures boost pressure and temperature and sends this information to the ECU. This then controls the level of vacuum in the VNT control diaphragm via the boost control solenoid.

 

Now, in first and second gears, the rate of rise of the engine speed is comparatively high, and a sticky VNT mechanism may tend to stick in the 'high boost' position a little too long, causing the ECU to keep calling for reduced vacuum, until a point at which the VNT mechanism suddenly moves to a 'low boost' position. This will cause a temporary reduction in engine power. The ECU then calls for an increase in boost pressure until normal service is resumed.

[littledaz]

Mardle,

 

which area of the country are you in?

 

Your Gal could benefit from a Vagcom plugin. Faults could lie with MAF, turbo, throttle position sensor, fuelling. As others have said, we need a little more info. Does it play on gradients, when hot or cold (eng temp), warning lights, etc?

[Mardle]

Thanks for the suggestions it is greatly appreciated. I am based in Norwich. Basically the car runs absolutely fine apart from the one problem mentioned. It starts OK and runs smoothly without any missing or harshness. The only snag is this hesitation. The strange thing is the car actually seemed to be performing better than ever recently which would seem to tie in with Tim's suggestion. When the car is stone cold there is no hesitation. Once the temp gauge reaches 60 upwards the symptom will appear. Pull away from a roundabout or traffic lights with an average throttle opening, (remember i'm the one who gets good milages out of Dunlops so lets change that to conservative opening), and the car pulls really well, normally up to about 1700 revs or so. Bit hard to be exact as the rate increases quite quickly in first. The engine will then suddenly lose power. It doesnt cut out its just as if you have reduced the throttle opening. Keep your foot on the same place on the throttle and it will suddenly zoom away again always within a second or so of the fault occuring. If you hold first this pattern may be repeated at 2500 rpm or so but I would normally go to second at this point anyway. Symptom is then repeated in second but not the higher gears. Once up to speed, say 70 on a dual carrageway, the car will sit on cruise control and perform perfectly. The fault only occured after I cahnged the run on pump, (yes brushes down to the wire). I have looked at all of the pipes in this area and they all seem in place and tight but I will double check as it seems too much of a coincidence. I will also check all of the electrical connectors in that area. There is no engine management light on. Will keep you posted how I get on. If all else fails I will book it in and let you know what the cure is.

On a seperate note this forum has been great since I found it. It has saved be a fortune on the aux pump and I also checked the wiper linkages after reading so many posts. When I took them apart the passanger side one was close to solid. Now all copper greased.

 

2001 , Diesel 115bhp, Galaxy Ghia, 96K hoping to keep to 130K at least. (Kids to fund through uni)

[tim-spam]

I know you shouldn't really do this, but what happens if you rev the engine fairly hard when cold - say in second or third gear to around 3000 - 3500 rpm. If the engine feels very rough and / or trips into limp mode, this would confirm a sticky VNT mechanism. You may find that the engine becomes rough and then suddenly smoother if the VNT frees up.

 

By the way, if the engine does trip into limp mode, lift your foot off the accelerator (whilst still in gear), key off and then on again (without operating the starter!). This will reset the ECU and normal operation will be resumed.

 

VAGCOM will then show a 'boost pressure positive deviation - intermittent' DTC.

[Mardle]

Tim thanks. Not in a position to test at the moment but will let you know what happens.

[Mardle]

Took to 3000rpm. Did not cut out but repeated the hesitation and then pull at approx 2400 . Also tested on downhill section and found that if I can get the revs to increase quickly enough in 3rd it will do the same thing. Think I will now double check all connections at the weekend in daylight, if this fails I will drive around for a few more weeks and see what happens. If it continues or worsens I will get it booked in and let you know results. Thanks for the help.